In a conventional four cylinder internal combustion engine, balancing of the secondary inertia forces is of a main concern. In many applications, a pair of axially positioned counter-rotating balancing shafts are used to cancel the secondary forces. The secondary forces are produced by the piston and the connecting rod connected to the crankarms of the crankshaft. These forces are basically reciprocation forces and are essentially directed in a vertical plane. They are brought into existence by the angularity of the connecting rod and the varying ratio of the rod to the crankarm length and these forces are produced at a rate of twice the frequency of the engine speed. Accordingly, these forces are considered forces of secondary order since their frequency is twice that of the engine speed with the secondary forces being twice the frequency of the primary forces. The secondary forces operate in the same direction and each crankarm and connection rod produces forces of the same magnitude and in the same direction. The result of the secondary forces in a four cylinder engine of this design is four times the forces of any one cylinder in the engine. Accordingly, the unbalanced secondary forces, gas loads and minor manufacturing imperfections can develop a considerably resultant of force which cause the entire engine to vibrate, roll, pitch and yaw and a balancing system is normally incorporated in the engine.
In addition to the internal engine generated forces, external forces are applied to the engine. For example, when the engine is used to power a piece of earthmoving equipment impact forces from the working of the equipment are transmitted to the engine. These forces may be transferred in a direction axial to the balancer shaft whereas internal forces are normally transferred perpendicular to the rotational direction of the shaft. The shafts of such balancers are normally constrained in an axial direction by a rigid member which transfers these impact loads from the machine to the balancing system. One such positioning member is disclosed in U.S. Pat. No. 4,425,821 issued to Floyd G. West on Jan. 17, 1984. The shaft is rigidly positioned in a housing by a washer and snap ring combination at one end and a gear and screw combination at the other end.
Another example of a rigid positioning system is disclosed in Caterpillar Parts Book for a 3304 Industrial Engine published in July of 1978 and shown on pages 23 and 25. The balancing shafts are positioned in the block by a pair of plates secured to the block and positioned in grooves in the shafts.
Thus, what is needed is a positioning system or an isolating device that can isolate both internally and externally induced forces from the balancer system or a rotating shaft. Furthermore, the device must be able to resist wear and provide adequate service life.